Interrogators choice really. People trying to recruit captured guards or playing the Good cop of the Duo might default to Diplomacy. While the Bad cop necromancer might decide Intimidate is faster. A fast talking con artist bard might lie about their circumstances in aw ay that might trick them into revealing something with Bluff and an introspective Monk might just quietly use Sense motive to obatain information that they don't even know they're revealing.

Or you know somebody can just cast speak with dead and skip this whole minigame.

Also depends on how literal the game mechanics are with "interrogation". As usual, I don't know this system except for the most basic bits, but what I am used to is there being several "social influence" skills. Fast-Talk, Diplomacy, Interrogation, and Sex-Appeal for the direct approach, with additional rolls allowing for an indirect approach (like Acting for a more convincing deception, but which would also require planning things out since its more than just a quick lie like Fast-Talk).

Speak with Dead does not or should not work for interrogation in most versions of the game. As has been noted, if the dead can remember what we want to know, he can remember that he doesn't want to tell us.